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Dave (O_D), "Motor Trend" was the cue which leads to the 1952 image below.




[source: Motor Trend] Click to enlarge!

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If I'm reading both the 52 and 55 Mobilgas figures correctly, then there are two numbers that really stand out. The 52 Lincoln Capri and the 55 Cadillac. Both had the four speed Hydra-Matics that could beat other transmissions in solid slip-free hook ups and that overdrive fourth gear. And, if my memory is correct, the Lincoln might have been in the first year of the new overhead valve V-8, a year or two before its Mercury and Ford brethren got theirs. Still, these two cars were really ahead of the competition.

My uncle had a new 55 Buick Century hardtop. He maintained that any time he had that car get better than ten mpg was a good day. Then he'd quickly add that if you worried about gas mileage while driving a fine car, then you had no business driving it. Of course, gas was 22 to 25 cents a gallon.

Sometime in the 1950s, I remember reading either a Popular Mechanics or Popular Science article on how Mobilgas supervised drivers in their annual competition. No coasting or switching off the ignition at lights, although a very light feather foot was used by all on the gas pedals. One writer said that Smokey Yunick would listen to the possible Ford vehicles at the end of the assembly line just to get the best sounding valve trains before the Mobil officials picked the car and sealed the hood. I wonder if the Cadillac and Lincoln people did even more to get those numbers?

HydraMatic's highest gear was an "overdrive"? Forgive me if I'm wrong but I'm certain it was not, it was just 1:1 direct drive.

I think you're correct about Hydra-Matics not having an overdrive fourth gear. It just felt like one, compared to PowerGlide, Dynaflow and of course, our Ultramatic.

A neighbor had a 1955 Olds Super 88 that would knock your teeth out with brutal shifts. Something might have been out of adjustment because another neighbor's new 56 Cadillac was much smoother. All things considered, including the propensity to leak fluids, I don't know which transmission caused more comments, Ultramatic or Hydra-Matic. GM surely sold them in strange places, so that might be the answer.

They didn't call early Hydramatics "leap and lurch" for no reason.

Are "Ton Miles" defined anywhere? To me a ton mile is 2000 pounds moved one mile.

I've handled shift complaints in Hydramatic vehicles, and when using the Hydramatic manual procedure, the results were impressive positive shifts. Getting the kickdown to work as well. The lack of a reaction member requiring the immediate shift after breakaway may seem quirky, but when working right it is no more intrusive than a modern trans.

I love the Hydramatic. On paper it should be a disaster, but in execution it is terrific. That kind of engineering triumph doesn't happen very often.

The biggest issue with figures like those in the '55 Motor Trend "controlled" tests is that with a typical margin of error, like ? 2 mpg, there's very little difference that can't be accounted for by rolling resistance and aerodynamics at higher speeds, and driver technique at lower speeds.

Look at the averages between Low-Medium Priced and High-Priced cars in '55. Considering the variance in weight in these cars, it's amazing how close they are in gas mileage. I think this might show something significant, though--better engines in the high-priced, heavy cars overcoming the weight handicap. It's pretty amazing, as heavy as cars got over the ensuing years, how efficiently the OHV V8 engine could move these bricks.

One thing to keep in mind when looking at those mpg figures is that, if you're using today's 10% ethanol gasoline, results will most probably be 6-10% lower mileage due to the lower "energy content" of ethanol.

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If I recall correctly the Hydramatic was revised in 1956 to make it a smoother shifting transmission. This was a major engineering change which included a 'Park' function like was found on many other automatic transmissions. Sorry, but I do not remember the improvement details.

(o{}o)

The biggest difference was the use of a second hydraulic coupling between the motor and the transmission. The earlier Hydramatics used just a single coupling. This change "cushioned" shifting. Internal modifications were ongoing to smoothe things out, too.